The present invention relates broadly to a nonlinear optical apparatus, and in particular to an optical fiber apparatus which is embedded in a nonlinear optical material.
In the field of fiber optics and fiber optic devices, there are a variety of techniques and materials that are utilized to accomplish the transmission of light signals in a controlled and reproducible xanner. Exemplary in the art of fiber optics and fiber optic devices are the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 3,455,625 issued to Brumley et al on July 15, 1969; PA1 U.S. Pat. No. 4,011,007 issued to Phaneuf et al on Mar. 8, 1977; PA1 U.S. Pat. No. 4,354,735 issued to Stowe et al on Oct. 19, 1982; PA1 U.S. Pat. No. 4,431,263 issued to Garito on Feb. 14, 1984; and, PA1 U.S. Pat. No. 4,461,536 issued to Shaw et al on July 24, 1984.
The Brumley et al reference, U.S. Pat. No. 3,455,625, discloses an optical coupling system for coupling a plurality of bundles of optical fibers to achieve a single light transmitting bundle without significant attenuation of the light. The apparatus is further characterized by the coupling material which conforms to the shape of the end of each fiber bundle so that the individual fibers in the bundles are contacted to provide a continuous optical path from input fibers to output fibers. The Stowe et al reference, U.S. Pat. No. 4,354,735 relates to an acousto-optic transducer which utilizes an optical fiber core having a first refractive index profile and an optical cladding encircling the core and having a second refractive index profile different from that of the optical fiter core. The transducer is arranged so that spatial average of the core refractive index profile is only slightly greater than that of the cladding refractive index profile. Thus, light is caused to propagate in the core with effectively minimum loss thereof to the cladding.
The Phaneuf et al reference, U.S. Pat. No. 4,011,007 describes an optical fiber bundle image conduit which utilizes a plurality of optical glass cores of selected refractive index and dimension that are clad with a first glass of lower refractive index providing substantially total internal reflection within the cores. The clad cores are then clad with a glass displaying a lower viscosity than either the core or the first cladding and fused into a final assembly. The cross-sectional area of the second core cladding is selected to provide a minimum free space within the fused assembly.
The Garito reference, U.S. Pat. No. 4,431,263, discloses materials that are useful in the elaboration of thin film, single crystal and other devices. The invention describes nonlinear optical and other materials that are suitable for use in electro-optical, second harmonic generating, electro-acoustic, piezoelectric, pyroelectric, waveguide, semiconductcr and other devices especially those wherein arrays or aggregates of films or layers may be employed as constituents.
The Shaw et al reference, U.S. Pat. No. 4,461,536, describes a fiber coupled displacement transducer apparatus that utilizes the sensitivity of a fiber optical coupler to mechanical displacement of its coupler elements as the basis for an extremely high resolution, non-electromagnetic displacement transducer.
Additional prior art references that are pertinent to the present invention are:
(a) Charles J. Koester et al, Amplification in a Fiber Laser, Applied Optics, Vol. 3, No. 10, October 1964.
(b) Charles J. Koester, Laser Action by Enhanced Total Internal Reflection, IEEE, Journal of Quantum Electronics, Vol. QE-2, No. 9, Septembr 1966.
(c) Roger H. Stolen et al, Paraxetric Amplification and Frequency-Conversion in Optical Fibers, IEEE, Journal of Quantum Electronics, Vol. QE-18, No. 7, July 1982.
(d) G. H. Hewig et al, Frequency doubling in a LiNbO.sub.3 thin film deposited on sapphire, J. Appl. Phys. 54(1), January 1983.
(e) Bridges et al, Liquid Core Fibers, Opt. Letters 6, 632 (1981).
Previous nonlinear optical fibers have relied on 4-wave xixing in glass fibers (R. Stolen and J. Bjorkholm, IEEE J. Q. E., QE-18, 1062 (1982)), doping of glass fiber claddings (C. Koester, IEEE J. Q. E., QE-2, 580 (1966)) or cores (C. Koester and E. Snitzer, Appl. Opt. 3, 1182 (1964)), or liquid core fibers (Chraplywy, T. Bridges, A. Opt. Lett. 6, 632 (1981)). However, no second order processes like phase-matched frequency doubling have been reported for single crystal hybrid single crystal fibers because these devices have not been available until now. Although planar waveguides have been used for frequency doubling (G. Hewig and K. Jain, J. Appl. Phys. 54, 57 (1983)), their efficiency is limited by short interaction length, a problem which is solved by the embedded fiber devices. It may also be noted that the use of planar guides in fiber optic systems is hampered by low damage thresholds and high coupling losses.
The purpose of the present invention is to perform second order nonlinear optical signal processing in amorphous glass fibers. Therefore, any apparatus that is utilized in a low power lasers such as frequency generators and "in-line", all-optical signal amplifiers operating in a parametric fashion can be realized using this invention.
This invention also addresses a major problem in fiber optical communication schemes. Currently, most integrated optical data processors and nonlinear optical processors are fabricated on planar structures. However, there exist major practical (i.e. mechanical) and fundamental (mode matching) problems in achieving low loss coupling of radiation in fibers with these planar devices. With this invention, the embedded fibers act as the guiding stuctures, and thereby minimize coupling losses. The present invention is intended to satisfy that need.